The Aerobic system

kicks in during low- to moderate-intensity as the arrival of sufficient oxygen enables continued energy production. this system utilises around 95% of the potential energy in glucose through three distinct stages:

  1. aerobic glycolysis

  2. Kreb’s cycle

  3. Electron transport chain (ETC)

Aerobic Glycolysis:

converts glucose into pyruvic acid with the enzyme PFK (phosphofructokinase) catalysing the reaction. this releases enough energy to resynthesise 2 moles of ATP. converting glycogen into glucose using GPP (glycogen phosphorylase) maintains this process for extended periods of time.

  • as oxygen is now in sufficient supply, the pyruvic acid is no longer converted into lactic acid. instead it goes through a link reaction catalysed by coenzyme A, which produces acetyl CoA - allows access to the powerhouse of the muscle cell, the mitochondria (where aerobic respiration and energy production occur)

Kreb’s cycle:

acetyl CoA combines with oxaloacetic acid to form citric acid, which is oxidised through a cycle of reactions

CO2, hydrogen and enough energy to resynthesise two moles of ATP are released, which occurs in the matrix of the mitochondria

Electron transport chain:

hydrogen atoms are carried through the electron transport chain along the cristae of the mitochondria by NAD and FAD (hydrogen carriers). they split into ions (H+) and electrons (H-)

the hydrogen ions are oxidised and removed as H20.

pairs of hydrogen electrons carried by NAD release enough energy to resynthesise 30 moles of ATP and other carried by FAD release enough energy to resynthesise 4 moles of ATP

  • overall yield of the ETC is 34 moles of ATP

Stages combined:

with all three stages combined;

  • one mole of glucose yields 38 moles of ATP

a highly efficient and most preferable energy system used for activities. the higher the performer’s aerobic capacity, the faster oxygen will arrive in plentiful supply and the switch can be made to aerobic energy production

breakdown of glucose:

  • Glucose + 6O2 → 6CO2 + 6H20 + energy

resynthesis of ATP:

  • energy + 38P + 38ADP → 38ATP

breakdown of ATP:

  • ATP → ADP + P + energy for muscular contraction

The aerobic system and FFAs:

glycogen stores are large and will fuel the aerobic system for a significant period of time. but long distance performers will want to reserve glycogen stores because they can be broken down both aerobically and anaerobically for higher-intensity sections of events or games.

triglycerides or fats can also be metabolised aerobically as free fatty acids (FFAs), providing a huge potential fuel store which conserves glycogen and glucose for higher intensity sections

on the release of lipas (enzyme responsible for catalysing the breakdown of fats) triglycerides are converted intp FFAs and glycerol. FFAs are converted into acetyl CoA and follow the same path through the Kreb’s cycle and ETC as pyruvic acid

  • FFAs produce more acetyl CoA and a higher energy yield → preferable for long-distance athletes whose events last more than an hour.

  • however, FFAs require around 15% more oxygen to metabolise and consequently the intensity of exercise must remain low

type of reaction; aerobic

food fuel used; glycogen/glucose and triglycerides (FFAs)

  • one mole of glycogen yields 38 moles of ATP (1:38)

by products; CO2 and H20

Pros of the Aerobic system:

  1. no fatiguing by-products

  2. high ATP yield

  3. long duration of energy production

  4. large fuel stores - triglycerides, FFAs, glycogen and glucose

Cons of the Aerobic system:

  1. delay for oxygen delivery and a complex series of reactions

  2. slow energy production - limits activity to sub-maximal intensity

  3. demand for O2 - triglycerides or FFAs demand around 15% more O2 for breakdown